how to check datastorage size before exceed usage size

Dear

we have two vmware server ( vSphere 4.1) with shared SAN stoarge ( EMC AX4-5) with 2TB lun that assign each one to each server.

in vnware server we have 5 VM mchine that use these shared space to manage and store own data.

i afraid about how can i check shared data storage before to reach maximum size and drop our vm machine for low disk space.

i would like to know that checking must be do in SAN level or in VMware level.

please let me know how can i do this?

regards,

Mahdi Bashiri